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Preventing Vitamin D Deficiency in Vulnerable Preterm Infants

By Julia Bird

Infants born preterm are at greater nutritional risk for three reasons. First of all, their early birth means that they are born without all organ systems and facilities working and as well as an infant born at term. For example, the coordination of sucking and swallowing needed for proper feeding until 34 weeks gestation, which means they require additional support to help them feed. Secondly, they have a higher chance of other complications including life-threatening infections that increase the need for nutrition whilst interfering with appetite and ability to feed. Thirdly, they miss out on the transfer of many essential nutrients that occurs in the third trimester of pregnancy (see our post from November 13, 2013).

Low levels of vitamin D are also a problem in preterm infants. Recently, Natarajan and co-workers conducted a clinical study looking at preventing vitamin D deficiency in preterm infants via supplementation. The authors supplied either 400 IU or 800 IU vitamin D to 94 infants born between 28 and 34 weeks gestation at a neonatal unit in northern India. 87 infants completed measurements to 40 weeks gestational age, and 80 infants were followed to 3 months corrected age, which is the age the infant would have been if born at term. Infants were enrolled if they were receiving enteral feedings by two weeks’ of age and did not have other significant problems. Doses were adjusted according to whether the infant was receiving human milk fortifier or formula, as these sources of infant nutrition contain supplemental vitamin D. Sunlight exposure was not determined.

The authors found a high rate of vitamin D deficiency in the infants at baseline. Around 80% thus had vitamin D levels lower than 20 ng/ml. This is in agreement with other studies conducted in infants, such as those from Burris, Fares, and McCarthy; rates of vitamin D deficiency were higher in preterm compared with term infants. At the measurement point that coincided with 40 weeks of gestation, the rates of vitamin D deficiency had dropped, with only 40% of the group supplemented with 800 IU vitamin D classed as deficient, compared to 65% in the group supplemented with 400 IU vitamin D. At three months corrected age, vitamin D deficiency rates had decreased further and only 12.5% of the higher dose supplemented group were deficient, compared to 35% in the lower dose group. One infant in the group supplemented with 800 IU vitamin D had extremely high levels of vitamin D by the end of the study, although there were no signs of hypercalciuria or kidney stones, and the infant was asymptomatic.

The results of this study show that the incidence of vitamin D deficiency can be reduced with supplementation of both 400 IU and 800 IU vitamin D. The higher dose is more effective, however there is a chance that blood levels can increase beyond normal levels, and therefore should be monitored. Despite this, 12.5% of infants remained vitamin D deficient even after over 3 months’ supplementation with 800 IU vitamin D. Regular monitoring of the nutritional status of preterm infants will give the best indication of whether the supplementation regimen is effective in normalizing vitamin D levels.